the produced flows were relatively slow flows that had little capacity to pass above topographic obstacles or to move rocks around. It nevertheless spread over large distances, since the topography of the region had been flattened by the previous Toconquis ignimbrites, and was still hot by the time it came to a standstill. Pumice is scarce and usually present in only small fragments, and lithic fragments are also uncommon except at the bases of the deposit. Fiamme structures on the other hand are fairly common especially where the ignimbrite crossed river valleys. The ignimbrite displays varying degrees of welding but has often spectacular columnar joints. At first it was assumed that this ignimbrite crops out over a surface of but later it was found that it covers a surface closer to . Between the intracaldera ignimbrite, the parts of the ignimbrite that extend away from the caldera and outcrops at large distance, the volume is about , down from earlier estimated of volumes exceeding but the Galán eruption is still one of the biggest known volcanic eruptions and the volcano has produced almost half of the volume of ignimbrites in the southern Puna. The Galán ignimbrite is the largest ignimbrite erupted by this centre; there is a tendency of the volume of individual ignimbrites to increase as the volcanoes grow younger, not only at Galán but also at other Puna ignimbrite centres, and this may be a consequence of progressive changes in the crust. Such giant eruptions have not been observed during historical time and are considered to be among the most dangerous volcanic phenomena known. Kay et al. proposed that the Galán ignimbrite consisted of three separate units, an intracaldera one emplaced 2.13 million years ago and two extracaldera ones 2.09 and 2.06 million years ago. Post-Galán volcanism The main Galán caldera formed during the Galán ignimbrite eruption, and it is possible that the collapse of the magma chamber roof actually started the eruption. Later it was found that a trapdoor collapse is a more plausible interpretation of the caldera structure and that the caldera appears to be much smaller than its present-day topographic expression. Most likely a lake formed within the caldera after its eruption. Later volcanic activity resulted in lava flows of dacitic composition being erupted along the ring fault of the caldera, as well as the formation of the resurgent dome by about uplift along the